The tunneling current from a scanning tunneling microscope was used to image and dissociate single O{sub 2} molecules on the Pt(111) surface in the temperature range of 40 to 150K. After dissociation, the two oxygen atoms are found one to three lattice constants apart. The dissociation rate as a function of current was found to vary as I{sup 0.8{plus_minus}0.2} , I{sup 1.8{plus_minus}0.2} , and I{sup 2.9{plus_minus}0.3} for sample biases of 0.4, 0.3, and 0.2V, respectively. These rates are explained using a general model for dissociation induced by intramolecular vibrational excitations via resonant inelastic electron tunneling. {copyright} {ital 1997} {ital The American Physical Society}

Single Molecule Dissociation by Tunneling Electrons

The formation of single-layer-thick molecular networks at metal surfaces is governed by the interplay between intermolecular and interfacial interactions. This Review highlights how, with films built by vacuum deposition, these interactions can be modulated to form substrates that may be useful as catalysts or templates for further deposition steps.

Tailoring molecular layers at metal surfaces

Manipulation of individual atoms and molecules by scanning probe microscopy offers the ability of controlled assembly at the single-atom scale. However, the driving forces behind atomic manipulation have not yet been measured. We used an atomic force microscope to measure the vertical and lateral forces exerted on individual adsorbed atoms or molecules by the probe tip. We found that the force that it takes to move an atom depends strongly on the adsorbate and the surface. Our results indicate that for moving metal atoms on metal surfaces, the lateral force component plays the dominant role. Furthermore, measuring spatial maps of the forces during manipulation yielded the full potential energy landscape of the tip-sample interaction.

/pdf/the-force-needed-to-move-an-atom-on-a-surface-37awt0l5c5.pdf

The force needed to move an atom on a surface.

At the “Molecular Rotors and Motors” symposium of the Spring 2009 ACS National Meeting in Salt Lake City (March 22−26), a diverse mix of talks addressed many current issues in the field. Speakers described topics that varied from single-molecule rotors and nanomachines to exquisite synthetic approaches toward building functional materials and mathematical and computational methods aimed at uncovering design opportunities and highlighting the fundamental limitations of molecular motors. While the realization of building useful nanomachines remains far off, a general consensus abounded that investigating biological systems and understanding the implications of the laws of thermodynamics and quantum mechanics for the behavior of nanostructures will help drive important advances in the quest for molecular machinery. Molecular rotors were demonstrated to have practical applications as probes for microviscosity, and many speakers presented experimental studies that indicated that highly directed translation and...

https://pubs.acs.org/doi/pdf/10.1021/nn900411n

Molecular rotors and motors: recent advances and future challenges

Gold adatom as a key structural component in self-assembled monolayers of organosulfur molecules on Au(1 1 1)

Incomplete coverages of p-fluorothiophenol, p-chlorothiophenol, and p-bromothiophenol form ordered islands on a Cu(111) surface even at low temperatures. The complexity of the molecular patterns increases from a simple (3 x 4) superlattice to a honeycomb (8 x 8)R19 degrees structure with increasing substituent electronegativity. We propose a model based on quadrupolar intermolecular interactions to account for this observation.

http://research.chem.ucr.edu/groups/bartels//publications/jacs126p7762.pdf

Effect of Halo Substitution on the Geometry of Arenethiol Films on Cu(111)

We investigated the adsorption of 2,5-di-chloro-thio-phenol (DCTP) on Cu(111) at 15 K and the formation of the thiolate upon electronic and thermal excitation. Initially, the sulfur atom of DCTP adsorbs at an on-top site and the molecule is able to rotate through six almost identical surface orientations. Attachment or removal of electrons from anywhere within the molecule at several hundred mV bias leads to the abstraction of the hydrogen atom from the thiol group in a nonthermal one-electron process with perfect selectivity. The resultant thiolate is locked into position on the surface.

2,5-dichlorothiophenol on Cu(111): Initial adsorption site and scanning tunnel microscope-based abstraction of hydrogen at high intramolecular selectivity

Para-halosubstituted thiophenols (X-TPs, where X is Br, Cl, or F) form ordered islands and monolayers on Cu(111) at temperatures as low as 81 K. At incomplete coverages, all X-TPs adsorb with the dehydrogenated thiol group attached to the substrate and the substituted ring inclined toward the surface, as verified experimentally and theoretically. The structure of ordered islands has a pronounced dependence on the nature of the halogen substituent:  while unsubstituted TP and pentafluoro-TP molecules do not self-assemble into extended ordered patterns at 81 K, X-TP molecules form a range of different structures which depend both on the size and electronegativity of the substituent, as well as on the coverage.

Halogen-substituted thiophenol molecules on Cu(111).

We present data on the coverage and nearest-neighbor dependences of the diffusion of CO on Cu(111) by time-lapsed scanning tunneling microscope (STM) imaging. Most notable is a maximum in diffusivity of CO at a local coverage of one molecule per 20 substrate atoms and a repulsion between CO molecules upon approach closer than three adsites, which in combination with a less pronounced increase in potential energy at the diffusion transition state, leads to rapid diffusion of CO molecules around one another. We propose a new method of evaluating STM-based diffusion data that provides all parameters necessary for the modeling of the dynamics of an adsorbate population.

http://research.chem.ucr.edu/groups/bartels/publications/jcp123p201102.pdf

Coverage and nearest-neighbor dependence of adsorbate diffusion

We present a low-temperature scanning tunneling microscopy study of increasing coverages of 2,5-dichlorothiophenol, an asymmetrically halo-substituted aromatic thiol, on Cu(111). At low coverage, deprotonation of the thiol occurs spontaneously upon adsorption at 80 K. Albeit the low deposition temperature, we find the formation of adsorbate islands at low coverage, which coalesce into a well-ordered film of horizontally adsorbed molecules at increasing coverage. This behavior indicates (i) significant mobility of the thiols on Cu(111) even at low temperatures and (ii) attractive adsorbate-adsorbate interactions. At higher coverages intermolecular interactions prevent long-range diffusion of adsorbates and thermal activation of the S-H bond becomes necessary. A close analysis of the molecular films reveals chiral recognition between neighboring molecules, which leads to the formation of enantiopure areas on the surface. Upright orientation of individual molecules starts at the boundaries between such phases and can be induced by scanning tunneling microscopy.

http://research.chem.ucr.edu/groups/bartels//publications/langmuir20p4406.pdf

Bommisetty V. Rao

Papers

Effect of Halo Substitution on the Geometry of Arenethiol Films on Cu(111)

2,5-dichlorothiophenol on Cu(111): Initial adsorption site and scanning tunnel microscope-based abstraction of hydrogen at high intramolecular selectivity

Halogen-substituted thiophenol molecules on Cu(111).

Coverage and nearest-neighbor dependence of adsorbate diffusion

Low-temperature mobility and structure formation of a prochiral aromatic thiol (2,5-dichlorothiophenol) on Cu(111).